Already known through British patent specification No. 1 245 906 is an explosive shell case with pre-shaped fragments, preferably in the form of balls of metal with high density, which are baked into a suitable plastic between a metallic inner and outer sleeve.
Since the shell must be able to absorb high pressures from the propellant charge and high centrifugal forces from the rotation of the shell, i.e. both axial and radial forces, exacting demands are imposed on the strength of the shell case. The material in the shell shall also be able to function upon detonation of the shell as a propelling surface for the pre-shaped fragments and contribute to their acceleration to a high and uniform velocity.
These requirements have, however, been difficult to combine. In the aforesaid explosive shell case, for example, the metallic outer sleeve imparts higher strength to the shell but at the same time prevents an increase in the velocity of the fragments upon detonation of the shell, which is a disadvantage.
In recent times, therefore, several different solutions have been proposed in order to provide a shell case which is sufficiently strong to absorb both axial and radial forces to which the shell is exposed but in which the fragmentation effect is nevertheless the greatest possible.
Proposed in the published Swedish patent application No. 72.07166-5, for example, is a fragment case produced in such a way that prefabricated fragments are pressed in through high-pressure deformation between concentrical tubes. Described in Swedish patent specification No. 76.09596-7 is a procedure for the manufacturing of a fragment case in which the fragments are baked into a fine-pore, compressible, sintered mantle and in the German Offenlegungsschrift No. 19 43 472 a fragment case is shown in which the fragments are included in a supporting sintered mantle but with residual cavities between the fragments which are possibly filled with a light material such as aluminium or plastic. Finally, described in the published Swedish patent application No. 77.02160-8 is a fragment case in which the fragments are pressed into a supporting frame of material made age-hardenable through sintering which surrounds the fragments on all sides of a solid shell base body.
In all of these examples the pre-shaped fragments are surrounded by partly soft or porous compressible material. A material of this nature facilitates baking in of the pre-shaped fragments but is not an ideal material with regard to either strength properties or ability to accomplish an effective fragmentation effect.
The object of the present invention is therefore to provide a shell case with good strength properties and a higher fragmentation effect. The invention is characterized to this end largely in that the material surrounding the fragments consists of a completely dense non-compressible material which is firmly united with the pre-shaped fragments.
According to one preferred embodiment of the invention the material surrounding the fragments (the carrying material) consists of a hardenable steel which, in course of manufacturing, is bonded to the fragments and together with these forms a connected jacket which surrounds the explosive in the shell.
The method of manufacturing the shell case is characterized largely in that the prefabricated fragments are imparted a permanent connection with the material in the case whereupon the shell blank is imparted its final properties through heat treatment.
According to one advantageous embodiment the case is made by a powder metallurgical procedure in which the material of the case in the form of a metal powder together with the prefabricated fragments is pressed under high all-round pressure and high temperature into a tight, compact jacket.